JPH0352890B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an apparatus for measuring the shape of a disk-shaped medium (hereinafter referred to as a disk) on which information is recorded.

<Prior Art> There is a type of disk called an optical disk, in which grooves called pits are arranged concentrically or spirally on the surface of the disk. Such disks have the following morphological errors with respect to theoretically accurate geometrical standards.

(1) As the disk surface rotates, the surface fluctuates up and down relative to the read/write head (hereinafter referred to as runout).

(2) The geometric center of the track (pitch row or pre-group) formed on the disk does not coincide with the center of the outer diameter of the disk (or the inner diameter if it has an inner hole in the center). (hereinafter referred to as eccentricity).

(3) The disk surface is not perfectly flat, but has an inclination (hereinafter referred to as warpage).

For this reason, the focal position of the optical detector on the surface of the rotating disk is three-dimensionally several hundred μm.
It will fluctuate irregularly within the range. Therefore,
If the deviation from the disk's geometric standard becomes large, the track and focus servo mechanisms will be unable to follow it, so a disk shape measuring device is used to check that the morphological error is within a certain tolerance. .

FIG. 4 is a configuration diagram showing the principle of the disk shape measuring device. In the figure, 1 is a disk, 2 is a turntable on which the disk 1 is placed, 3 is a shaft that supports the rotation of the turntable 2, 4 is a motor that drives the rotation of the turntable 2, and 5 is the disk 1
along arrow A in the radial direction of disk 1.
6 is a displacement transducer for measuring the radial displacement of the track formed on the turntable 2; 6 is a presser foot for pressing the disk 1 and fixing it on the turntable 2;
It is a means of movement that moves in a straight line.

In the device configured in this way, the disk 1 is rotated by the turntable 2, and
The output signal of the displacement converter 5 is processed to measure the eccentricity and roundness of the disk 1.

<Problems to be Solved by the Invention> However, with the above-mentioned conventional apparatus, it was not possible to accurately measure the shape of the disk 1 for the following reasons.

FIG. 3 is a geometric relationship diagram of eccentricity errors. In the figure, point O _T is the center determined by the track formed on disk 1, point O _D is the center determined by the shape of disk 1, and point O _S is the center of rotation of disk 1 placed on turntable 2. . The disk eccentricity δ of the disk 1 is represented by a line segment O _D O _T , but normally there is a discrepancy between the rotation center of the turntable 2 and the center O _D of the disk 1, and the line segment _D
A mounting eccentricity δ1 of the disk 1 expressed by O _S is generated. Therefore, when determining the disk eccentricity δ and roundness from the signal of the track displacement converter 5,
There was a problem in that the line segment _{D S} to be obtained could not be obtained and the pseudo eccentricity δ2 (represented by the line segment _{D S} ) was incorrectly obtained.

On the other hand, it is also possible to mechanically improve the positional relationship between the turntable 2 and the disk 1 to reduce the mounting eccentricity δ1, but since it is approximately equal to the disc eccentricity δ1 to be determined, ,
The problem was that there were too many obstacles to achieve mechanically.

The present invention solves the above-mentioned problem, and is a disk shape measurement method that can obtain a track displacement signal that does not include the placement eccentricity δ1 even when the disk 1 is placed on the turntable 2. The purpose is to provide equipment.

<Means for Solving the Problems> The present invention achieves the above object by providing a turntable that rotates with a disk placed thereon, and a distance from the center of rotation of the turntable to a track formed on the disk. A track displacement transducer for measuring the amount of rotation of the turntable, an angle transducer for measuring the rotation amount of the turntable, and a flat reference disk with no disk eccentricity are placed in advance, and the center (O _D ) determined from the disk shape and the top of the turntable are placed. The mounting eccentricity (δ1) with respect to the rotation center of the turntable (O _S ), and the angle between the base line defined on the disk and the eccentric direction (φ ₀ ), and a means for storing the mounting eccentricity and the angle formed, inputting the mounting eccentricity and the angle stored in the storage means, and calculating the rotation angle of the angle converter from the base line. This disk shape measuring device is equipped with an error elimination circuit that outputs an eccentricity correction signal determined from the angle (φ−φ ₀ ) and the amount of mounting eccentricity according to (φ).

The present invention is characterized in that the signal from the track displacement converter is corrected by the signal from the error canceling circuit to obtain the distance between the center (O _D ) determined from the disk shape and the track.

<Function> Each component of the present invention has the following function. When a disk is placed on a turntable, a measurement signal containing a pseudo eccentricity is obtained from the track displacement transducer when measuring the track. Therefore, the error canceling circuit outputs a signal that cancels the amount of disk eccentricity, and the track displacement converter outputs a signal that includes the amount of disk eccentricity.

<Example> The present invention will be explained below using the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, parts having the same functions as those in FIG. 4 are given the same reference numerals and their explanations will be omitted.

In the figure, reference numeral 8 denotes an angle converter whose purpose is to measure the rotation angle of the disk 1, and actually measures the rotation angle of the turntable 2. Reference numeral 9 denotes an error erasure circuit which outputs an eccentricity error in the placement of the disk 1 according to the rotation angle of the disk 1, and the eccentricity error is measured and stored in advance through a calibration test. 10
is a differential amplifier that takes the difference between the output v1 of the displacement converter 5 and the output v2 of the error canceling circuit 9, and 11 is an output terminal of the differential amplifier 10.

In addition, a circular hole is provided in the center of the disk 1.
It is fixed along a convex portion provided at the center of the turntable 2 for positioning the disk 1.

FIG. 3 is an explanatory diagram of the operation in the position shown in FIG. 1. In the figure, r0 is the radius of the track formed on the disk 1, r is the distance from the point O _S to the measurement point P of the displacement transducer 5 on the disk 1, and the φ0 direction is the point O _S
This is the reference direction that determines the angle φ of the point P using a base line that is determined to pass through the point O _D from .

First, by using a flat reference disk with no disk eccentricity δ (that is, points O _D and O _T coincide), the angle φ ₀ between the mounting eccentricity δ1 and the line segment _{D S} from the base line is determined. Measure.

Next, if the mounting eccentricity δ1 that occurs when placing the disc 1 on the turntable 2 and the disc eccentricity δ are both zero (that is, O _D = O _T = O _S and each store is in agreement) The output V1 of the displacement converter 5 is expressed by the following equation.

V1(φ)=r0 (1) where r0 is a constant. However, if there is a mounting eccentricity δ1, {rcos(φ−φ0)−δ} ² +{rsin(φ−φ0)−δ} ² =r0 ² (2) holds, so the output v1 is It is given by the following formula.

V1 (φ) = r0 {√1 − (0) ^{2 2} (−0) + (δ / r0) cos (φ − φ0)} (3) Therefore, the rotation angle φ of the disk is changed by the angle converter 8. Correspondingly, when the output v2 is sent from the error canceling circuit 9 to the differential amplifier 10, a signal free of eccentricity errors in the placement of the disk is output from the output terminal 11.

FIG. 2 is a block diagram showing another embodiment of the present invention. In the figure, the output of the error elimination circuit 9 is connected to the moving means 7. The moving means 7 interlocks the displacement transducer 5 so as to eliminate eccentricity errors in the placement of the disk.

Note that the present invention is not limited to the above embodiments. The output v1 may be the following equation (5) instead of equation (3). That is, in a digital audio disk, since r0 is about 50 mm and eccentricity δ is about 50 μm, the above equation (2) is transformed as follows.

V1(φ)=r0[1+(δ/r0)cos(φ−φ0) −(1/2){(δ/r0) ² sin ² (φ−φ0)} +(1/8){(δ/ r0) ² sin ² (φ−φ0)} ² ] (4) In this equation, the third term on the right side is a second harmonic with an amplitude of about 0.025 μm, which is within the measurement tolerance. Ignoring this, equation (4) becomes the following equation.

V1 (φ)=r0 {1+(δ/r0) cos (φ−φ0)} (5) Therefore, the error canceling circuit 9 may output a cosine signal expressed by the following equation.

V2 (φ) = δ・cos (φ−φ0) (6) In addition, as shown in the conventional example, when positioning the disk 1 in the radial direction using the presser foot 6, the angle converter 8 is disk 1 for 6
It is necessary to express it in terms of rotation angle. Furthermore, the signals from the displacement converter 5 and the angle converter 8 may be AD converted and stored on a computer, and then the eccentricity error may be corrected on the computer using equation (6) or the like.

<Effects of the Invention> As explained above, according to the present invention, the mounting eccentricity δ1 that occurs when a disc is mounted on a turntable is removed by comparison with a reference disc, so that a track that does not include this displacement signal can be obtained. Therefore, by processing this signal, the disk eccentricity δ and the track roundness can be measured with high precision, and the measuring device itself can be manufactured at low cost. Furthermore, if a disk manufacturer uses the disk shape measuring device, a high-quality disk with a small disk eccentricity δ can be manufactured.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram showing one embodiment of the present invention, FIG. 2 is a configuration diagram showing another embodiment of the present invention,
FIG. 3 is an explanatory diagram of the operation of the apparatus shown in FIG. 1. Fourth
The figure is a configuration diagram showing the principle of a disk shape measuring device. 1...disc, 2...turntable, 5...
...Displacement converter, 7...Moving means, 8...Angle converter, 9...Error elimination circuit.

Claims (1)

[Claims] 1. A turntable that rotates with a disk placed thereon, a track displacement transducer that measures the distance from the center of rotation of the turntable to a track formed on the disk, and a rotation of the turntable. An angle converter for measuring the amount and a flat reference disk with no disk eccentricity are placed in advance, and the center ( _O
and the center of rotation of the disc on the turntable ( _OS )
Measure the eccentricity of the disc (δ1) and the angle (φ ₀ ) between the baseline defined on the disc and the eccentric direction, which is a line segment with one end at the center of rotation of the turntable. A means for storing the amount of eccentricity and the angle formed; and a means for inputting the amount of eccentricity of the mounting and the angle formed by the storage means, and calculating the angle (φ) according to the rotation angle (φ) of the angle converter from the base line. φ−φ ₀ ) and an error canceling circuit that outputs an eccentricity correction signal determined by the amount of the mounting eccentricity, wherein the signal of the track displacement converter is corrected by the signal of the error canceling circuit. A disk shape measuring device characterized in that the distance between the center (O _D ) determined from the disk shape and the track is obtained.